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safe ruler/ ruler

The traditional metallic ruler with sharp angles (to keep precision) is a threat to our safety. The new ruler improves the dangerous right-angle to more safer obtuse angel, which could lower the odds of accidents. In addition, the new ruler, compare with the traditional ruler, is more precise since the scale of the front end hardly to be worn. What's more, it also possesses certain additional functions the traditional ruler without, for example, we can easily to measure the orthogonality of two surfaces or the height of objects.